In recent years, the so-called shoe pressing dehydration of a wet web by pressing one surface of the wet web placed on a felt member traveling at a high speed with a press roll while pressurizing the other surface with a pressure shoe through an endless belt, is widely used in a press part of a papermaking step, in order to improve the dehydration effect for the wet web. In shoe pressing, a belt endlessly formed by integrating a reinforcing substrate and a thermosetting polyurethane layer is employed in general. Also in a calender step of smoothing and glossing the surface of paper, employment of the aforementioned elastic belt has been recently studied. In addition the employment of the aforementioned elastic belt has been also studied as a sheet transfer belt for preventing a web break and stably transporting a wet web, particularly when performing papermaking at a high speed. Japanese Utility Model Laying-Open No. 59-54598, Japanese Patent No. 2889341, Japanese Patent No. 3045975 or the like discloses a typical structure of such a papermaking belt prepared by covering both surfaces of a fabric base with an elastic material. Japanese Patent No. 2542250 or the like discloses another typical structure prepared by embedding reinforcing yarns in an elastic material.
As an elastic material for the papermaking belt, a thermosetting polyurethane prepared by mixing a urethane prepolymer and a hardener with each other and hardening the mixture is generally used as disclosed in Japanese Patent No. 2889341, Japanese Patent Laying-Open No. 6-287885, Japanese Patent No. 3045975, Japanese Patent No. 3053374, Japanese Patent Laying-Open No. 11-247086 or the like, and 4,4′-methylene-bis-(2-chloroaniline) (hereinafter referred to as “MOCA”) is employed as the hardener in thermosetting polyurethane used for the papermaking belt.
Generally in shoe pressing, severe bending and pressing are repeated on the belt between the press roll and the pressure shoe, and hence a polyurethane layer forming the belt becomes disadvantageously cracked. This cracking is mainly caused on the outer peripheral surface of the belt coming into contact with the felt member or paper. While grooves are generally formed on the outer peripheral surface of a belt for a dehydrating press used in the press part for improving the dehydrating efficiency, the cracking is readily caused on the bottom edges and the top edges of these grooves in particular. A crack once caused tends to grow into a larger crack as the belt is used. In this case, lubricating oil stored between the inner peripheral surface of the belt and the pressure shoe externally leaks to exert a bad influence on the paper or cause a delamination of the belt. Thus, occurrence and growth of the crack causes a reduction in the life of the belt. Therefore, suppression of occurrence and growth of cracks is strongly demanded in relation to a papermaking belt employed for shoe pressing or the like. Further, delamination may result from weak adhesion between the fabric base and the polyurethane layer, and prevention of such delamination of the fabric base and the polyurethane layer is strongly demanded.